The present invention relates to a biosensor which can measure alcohol concentration by reacting with vapor-phase alcohol, a method for manufacturing a strip-type biosensor for measuring alcohol concentration, and a breath alcohol analyzer using the biosensor for measuring alcohol concentration. Conventional biosensors using electrochemical measuring methods have been made by immobilizing, as a membrane, enzymes or microorganisms on the surface of an electrode such as a H.sub.2 O.sub.2 electrode, an oxygen electrode, an NH.sub.4.sup.+ ion selective electrode or of ISFET. Such type of biosensors can detect and measure an electroactive compound formed as the result of a single or multi-step enzyme reaction.
U.S. Pat. No. 4,655,880 disclose a biosensor by which various kinds of oxidase are immobilized on a thick film amperometric electrode to measure an electroactive compounds. However, the biosensor using such electrochemical measuring methods has a drawback in that it should be used in a favorable condition for a biologicial reaction. That is to say, such biosensors can detect only liquid-phase sample.
To overcome such a drawback of the conventional biosensors, a gas measuring biosensor, which can measure a vapor-phase organochemical material, and the method therefor are disclosed in the Korean patent application No. 93-13482. This technology the method for manufacturing a biosensor having a structure in which an sensing membrane having a hydrogel layer on which an enzyme reacting with vapor-phase organochemical material is immobilized on the electrode of an amperometric device. Most breath alcohol analyzers are commercially produced using a gas sensor adopting an oxide semiconductor, e.g., TGS 822 gas sensor manufactured by Figaro Inc. of Japan. Examples of the breath alcohol analyzer include an alcohol checker manufactured by Figaro Inc. of Japan and a breath alert manufactured by Breath Alert MFG of U.S.A. Such breath alcohol analyzer technologies measure alcohol concentration contained in the gases generated during human exhalation in the range from 0.1 mg/1 to 0.8 mg/1, and displaying a drinking degree using a light emitting diode (LED). There has also been proposed a technology in which an alert sound is produced if a drinking degree is higher than or equal to a predetermined level.
The ground for measuring the drinking degree is based on an experimental report that alcohol concentration contained in 1 ml blood almost equals to that contained in 2000 ml exhalation, that is, the correlation between alcohol concentration in the exhaled gas and in blood.
Therefore, blood alcohol concentration is indirectly known by measuring alcohol concentration of respired gases after drinking, hence the drinking degree is determinable.
In order to determine a probable drinking and driving which can be a basis for cancelling a driver's license as well as prosecution, there is a need for a sensor for measuring exact alcohol concentration contained in exhaled gases in the range of 20 to 500 ppm.
A method for measuring a drinking degree using an enzymatic reaction is disclosed in the Japanese publication laid-open patent Nos. shows 60-196198 and shows 60-172298. These technologies measure alcohol concentration contained in aqueous solutions, e.g., saliva, using a strip-type test paper, to measure the drinking degree. The international patent WO88/01299 proposes a drinking measuring technology for measuring alcohol concentration contained in gases generated during respiration by the color change of the test paper.
However, there has not yet been proposed a technology for measuring a drinking degree using a biosensor.
The aforementioned conventional technologies for measuring alcohol concentration involve the following problems.
First, the conventional breath alcohol analyzers using an oxide semiconductor gas sensor adopting an alcohol reactive metal oxide such as SnO.sub.2, TiO.sub.2 or RuO.sub.2 have no selectivity for ethanol. That is to say, in general, those breath alcohol analyzers are considerably affected by combustible gases like automobile exhaust, LPG, cigarette smoke, or thinner.
Second, when drinking degrees are intended to be measured consecutively during a short time period, if alcohol concentration for a previous person is strong enough considerably to affect the next person's alcohol concentration, the measurement accuracy decreases. To avoid such an affect from the previous person, those breath alcohol analyzers should be used after a delay of a predetermined time once they are used, which does not allow measurement for many people during a short time period.
Third, the conventional breath alcohol analyzers are readily affected by ambient temperature and have serious measuring errors depending on measuring methods. Thus, the breath need to be calibrated every two or three months.
Fourth, most breath alcohol analyzers require that a person blow a strong breath into the inlet of the sensor for not less than three seconds for measuring the drinking degree. In such a case, saliva may be intermixed into the sensor, which makes the measurement unreliable. Also, the mixed saliva may cause problems for the sensor.
Fifth, since the conventional technology for evaluating the drinking degree using the enzymatic reaction should detect the color change by means of a material such as 2,6-dichloroindophenol, the measured drinking degree may vary depending on the operator, which causes a lack of precision or objectivity in measuring a drinking degree. Further, there is a problem in that another measurement must be performed for more precise measurement of the drinking degree.
Therefore, a portable breath alcohol analyzer using a biosensor for measuring vapor-phase organochemical material according to the present invention solves the following technological problems.
1. In a biosensor using an electrochemical principle, in order to measure a vapor-phase sample, i.e., detectable gas, the sensing membrane of the biosensor should provide an electrode system. The conventionally proposed gas measuring biosensor utilized a hydrogel for measuring a vapor-phase sample.
2. Electrons should be transferred easily between an enzyme layer immobilized on the upper portion of the sensor and the electrode so that sufficient electrical signals are generated during the reaction with the vapor-phase sample. For this purpose, an electrode manufacturing technology, an enzyme technology and the combination of those technologies should be realized.
3. The breath alcohol analyzer using a disposable biosensor should have excellent individual characteristics of the sensors so that the objectivity of the measured values can be secured. Conventionally, the amperometric devices using thick film technology have been manufactured. However, in this case, in order to form an enzyme immobilized layer, since an enzyme solution should be dropped on the upper portion of the sensors individually, mass production is difficult and excellent individual characteristics of the devices cannot be obtained.
4. Since biosensors should be continuously provided separately from the drunkometer, the storage capacity of the biosensors should be sufficient in view of the distribution period of the biosensors.
5. The method for measuring a drinking degree should be simplified using a portable breath alcohol analyzer and biosensor.